A successive approximation register (SAR) analog-to-digital converter (ADC) is a type of analog-to-digital converter that converts a continuous analog waveform into discrete digital representations by performing a binary search to converge to the closest quantization level of each sample taken of the analog waveform then providing a digital representations thereof.
SAR ADCs are among the most popular ADC architectures, and may be used in, for example, microcontrollers. A typical differential SAR ADC, including most on the market, have limited input common-mode range which can lead to reduced performance or failure if the input common-mode exceeds the SAR DAC's allowable range. This makes differential SAR ADCs less suited for applications where the input common-mode voltage cannot be controlled, like certain sensor applications, zero-crossing detection and more. This may be circumvented by using additional active circuitry, as shown in FIG. 2, to sample the input common-mode voltage and subtract it during conversion as so as to cancel out its effects. This however is costly in terms of current consumption and integrated circuit die area, and also puts limitations on the input common-mode rate of change allowed.